The invention pertains to an accumulator for accumulating a substantial length of a running web such that if the infeed to the accumulator is stopped or slowed for a short interval, the web in storage is paid out continuously to a web-utilizing device so the device has a constant supply and thus need not be stopped or slowed.
One common use of a web accumulator is where a web is fed from a primary supply reel and it is necessary to splice the leading end of the web from a standby supply reel to the trailing end of a web from the primary supply reel in a manner which will not cause interruption of the web supply to a web consuming or utilizing device. In some known accumulators there is a row of spaced apart rollers on a movable carriage which cooperate with another row of stationary rollers.
When the support with a row of spaced apart rollers is moved away from the stationary rollers and the web is looped around the two sets of rollers in serpentine fashion, a substantial length of web can be accumulated. During running of the web, the rollers will be urged to their maximum separation from each other for accumulating and storing a maximum length of web. If the supply of web to the accumulator is stopped for a short time, the tension due to drawing web from the outfeed end of the accumulator causes the sets of rollers to move toward each other while the length of web in storage is paid out. After infeed to the accumulator is restored, the sets of rollers separate again to accumulate and store another length of web.
The forces of gravity and the weight of the movable roller assembly must be considered when configuring such a system. When oriented horizontally, gravity applies bending and binding forces which resist motion. When oriented vertically, gravity applies a linear force which tends to push the moving roller assembly down.
In accumulators which "accumulate down", web tension must overcome gravity to pull web from the system. In accumulators which "accumulate up", the device used to induce tension must overcome gravity to raise the moving roller assembly. Where the tensioning device must overcome gravity, it must do so reliably. The tensioning force is taken from that part which exceeds the force required to overcome gravity. Where the weight is significant, the force must be significant and the margin for error is necessarily also significant. This means that any excess force required for overcoming friction and other inertial forces must be taken from that part of the force reserved for web tensioning. This reduces the resolution needed for making fine adjustments in tension. It can therefor be seen that a system in which gravity is not a factor would be capable of more accurate tension control and be effectively used with more fragile webs.
The consequences of friction and inertia may be appreciated when it is realized that the web may be running at a very high rate of speed when suddenly, for some reason, such as when making a splice, the infeeding web is stopped or decelerated. This change in web motion will result in a reaction by the components of the accumulator. Most notable of these reactions is the motion imparted to the movable assembly of the accumulator. Minimization and control of the inertia and friction associated with this reaction is an important desired attribute of such accumulators. There is an important need for a web accumulator which provides the benefits of low friction and minimized inertia, allowing it to handle the most delicate of webs at high speeds without breakage or loss of control.
Gravity can be made a non-factor by arranging the system in a balanced or counterbalanced mode. Counterbalances applied to a traditional accumulator add mass without adding storage. The moving roller assembly must still move at the same velocities and while the effects of gravity have been canceled, the web must accelerate the inertia of twice as much mass.